That size boxed with a tuning of 29Hz should sound really good.
Im mainly into caraudio for the SQ, and tune my boxes to lower frequencies. I usually have luck in maintaining sq while lower the power needed for woofers.
I think your woofer is to blame, instead of the enclosure and its tuning. That woofer is just goin to sound like that.
BTW: Im curious if you have a subsonic filter...and if so, try lower the frequency on it for more punchy bass. Just a little though. Another reason for the sluggish bass will be the points you set your lowpass filter at. For a nice non localized bass, I recommend tunning the the LP filter to 55-85 Hz.
And if your still not satisfied...try building a small sealed enclosure and see how that sounds, that mtx might just not like vented enclosures. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif